Two-way radio communication system



Nov. 9, 1943. E. w. HERoLD TWO-WAY RADIO COMMUNICATION SYSTEM 'FiledFeb. 28, 1942l ATTORNEY Patented Nov. 9, 1943 fA f UNTED t y'21332'.,7121 TWO-WAYRADIO COMMUNICATIQ e,

SYSTEM mawvarjcll W. Herma* verme, N. "J1, t0-

of Delaware Application February 2s, 1942, VSerienV No; niet ,.111apfeenee wit shan be meenemen `fixed reieto to @een filth., A. L halve'iridiateg etatio ground station. v`for' ein l' B when used fortransmission employs a microphone I8, a modulator l 6, and atransmitting ampler 28. The antenna 6 is connected both to the converter8 and the amplifier 20. In some instances, it may be unnecessary toapply the'output from the oscillator 2 directly to the receiverconverter 8 because the energy fed through the amplifier may be combinedvwith incoming signals and fed through the conductor 24 to the converter8.

Where the circuit arrangement isk as just mentioned, it will, of course,be desirable- )apparent that exclusive communication between to employin the converter unit, or in a subse-x" quent stage, filtering means forsuppressing the carrier and the oscillations of the local source 2. j

The oscillator 2 may be frequencycontrolled '1 by the incoming signalsin accordance with Wellknown practice. The automatic frequency controldevice 22 is, therefore, shown conventionally for this purpose. Althoughautomatic frequency control devices are Well known, reference is heremade to United. States Patent No. 2,121,103, granted June 21, 1938toS.W. Seeley for a comprehensive disclosure of how they may beconstructedand operated. I will now present a mathematical discussion of thetheoryof operation of my invention: Let fa=the frequency of the oscillator Iof station A, say4 210megacycles, for example. Let fb=the frequencyofthe oscillator 2 at station B, say,200 meagcycles.

, Let fithe frequency towhich the intermediate frequency amplifiers A7and 4 are tuned, say 10 megacycles. Then, Y Y,

Now if station A is transmitting, then station B can placeitself intwo-way communication with station A merely bytuning its own oscillator2 .so that reception of station A s signals will beproperly received. Bythe samey tuning operationat station B, ythe signalstransmittedtherefrom will be suitable for reception byk station A. It isessential to the successful operation of my system,I however, that bothstations maintain anI agreed-upon tuning of their intermediate frequencyamplifiers, both to the samel frequency.

If it is desired to change the intermediate frequency tuning` inaccordance with a prearranged schedule, basedon agreement as to time ofchange, or any other'system,'then an element of secrecy is'introducedinto the communication. Not knowing what intermediate frequency is to beused, an unauthorized receiver would be unable to pick up the incomingsignals without considerable search for the transmitting carrier, andmost probably would not be able to answer back.

It is not necessary that the same antenna 5 or 6 should be used both fortransmission and reception, but it has been shown as a'single antenna ateach station merely for thesake of simplicity. It may not alwaysbenecessary to employ an automatic frequency control such as the unit 22at either of the stations, but should any drift in frequency 4occur atone terminal, adjustment of the tuning of the oscillator at the otherterminal will automatically assure perfect two-Way communication,provided the intermediate frequency amplifiers 3 and 4 of thecorresponding stations are similarly tuned. o

In connection with automatic tuning, itshould be noted that correctionof the local oscillator serves additional purposes as compared withthose previously contemplated. That is to say,`auto and . to thoseskilled in the art.

the master station and any one outlying station could be obtained by theuse of differently tuned intermediatefrequency amplifiers anddifferently "tuned oscillators at'the outlying stations. Where thisidea.y iscarried out, station B can receive selectively from anyoutlying station such as A, A', etc., but would need to select a localintermediate frequency for its own intermediate frequency amplier tobein agreement with the fixed-frequency of the 4 I. F. amplifier at the.selected. outlying station.v After makingthis adjustment, two-waycommunication .would. berestablished` simply by listeningto the signalsfrom the selected outlying station and causing the localoscillatorofrequency at station B to bethereafter.automaticallycfrequency contro1led.,In orderito tunethe,local station to a frequencywhich the,A remotestation will accept, whileat the Sametime adjustingthe tuning of ^`the local Vstation tothefrequency which the remote station radiates, it siof c ourseneces-f saryto selectanintermediate frequency for Vthe localstation whichcorrespondsmwiththe intermediate frequency ofthefremote station. oneconsideration determines the adaptability@ the system for control ofboth stations from the one master, station. f Other modifications of theprinciple I have outlined will be readily apparenttothosefamiliar withsuperheterodyne, reception., 1 For example. a receiver may be adaptedtoireeive bothy signals which are lower yin 1frequency than the Vlocal9s.- .Cillator and those which erehgher than `the os.- cillator (theso-called image response),. Thus, a group of stationsmayintercommunicateandvany given station may act as a type A to someqofthe other Stationsvand as a type `Bftothe remainder- When twosuchsvstemspperate vwith different I. F. amplier frequencies onlywthose*stationsy within a givensystem A canestablisn two-way ommuniatiea, L ot,

The practical adaption Vof my ideadsv readily apparent to those skilledin the art andrthereappears to be no need for` further, description ofmodulation and power-amplicatdnequipment- 'Ihe system may beuappliedwith amplitude, .frequency or phase modulation-,and theintelligence to betransmitted may be sound, television, Vfacsimile oroffany other type capable of being converted into electricalcurrents orpotentials. In complexity, the system may range from the simplesttransceiver employing a single-tube, ,selfoscillating frequencyconverter; Withflocal modulation on the oscillatorand a` one-,tubevintermediate frequenysystem, yto a highly comple;

andmodulators, radio frequency amplification and multi-stageintermediate frequency amplification with automatic frequency controlliV/ My invention is tobe understood as-comprehending the variousmodifications Suggestedabove as well as others which might suggestthemselves Y l n The s copeI of the'irl-A vennen is, therefore. Adefinedbr the Claims- Y i I claim: t Y 1. A two-way ycommunication systemoperable between two radio stations, each station com,-

plier in the receiver, the intermediate frequency ampliers at the twostations being tuned to the .prising a transmitter, a superheterodynereceiver, .an oscillator Vcommon `to the transmitter `and Y thereceiver, and any intermediate frequency am-` i operable between tworadio stations, each station comprising a transmitter, a superheterodynereceiver, an oscillator common to the transmitter and the receiver, andan intermediate frequency tampliflervin the receiver, means foradjusting same frequency,' and means located at `one of l said stationsfor maintaining a vfrequency separation betweenthe outputl energies ofthe two said oscillators equal to the frequency to which saidintermediate frequency amplifiers are tuned.

2.,Asystem in accordance with claim l and including an automaticfrequency control device in the means for maintaining frequencyseparation.l v .l Y

3. A system in accordance with claim 1 and including anautomaticfrequency control device in the means for maintaining frequencyseparation and operable in accordance 4with Variations in the frequencyof the receivedl vcarrier wave.`

4. A two-way vcommunication system in accordance with the inventiondefined in claim 1,

wherein ther oscillator at one station .is adjusted to operate at afrequencyabove the signal frequency receivedsby said station and theoscilla'- tor at the otherstation is adjusted to operate at a frequencybelow the signal frequency received by said other station. t j

5. In a two-waylradio communication system wherein each of two stationscomprises a transmitter, a superheterodyne receiver, an oscillator thetuning conditions at only one of the stations to satisfy the'tunngconditions at both stations necessaryV for two-wayl communieationAtherebel tween, said means comprising` means' for tuning theintermediate frequency amplifier at'said one 'station to operate at theysame frequency as that l of the `intermediate frequency amplifier at theother station and additional means for main-v 'taininga frequencyseparation between the os-f cillators at thetwo stations equal to 'theoperating frequency ofsaid intermediate frequency ampliers. a

, 7.' The methodaeeordmg to claim 5 and including the step of causingthecarrier wave re- 'ceived at said one station to automatically controlthefrequency of the oscillator thereat. l

8- In ,a -radio communication. system having a master station andaplurality of outlying respondentv stations, wherein each station comeprises a transmitter, a superheterodyne receiver,

` (an oscillator common to the transmitter and the common to thetransmitter and the receiver,a`nd

an intermediate frequency amplifier in the receiver, the method ofadjustingthe tuning conditions at one station only, to satisfy thertuningr conditionsat both stations necessary fortwo-way` communicationItherebetween, which method comprises tuning the intermediate frequencyamplier at said one station tothe same frequency receiver and anintermediate frequency amplien. and wherein said master stationAincludes an automatic frequency control device operable upon itsoscillator to control the frequency thereof in accordance with anincoming carrier wavegthev method of adjusting the tuning conditions atsaid master `station lto satisfy the tuning'condi--` t vtions thereatandsimultaneouslyto establishtwo-I way communication between said masterstation and a selected ione of Asaid/respondent stations,

t whichtmethod comprises tuning the intermediate as that of theintermediate frequency amplifier at Y the other station,` andmaintaining afrequency separation betweenl the oscillators at the twostations equal to the tuning frequency of said I intermediate frequencyamplifiers. a Y

frequency amplifier at the master station to the same frequency as thatof the intermediate fre-i quency amplifier at said selected station,vand tuning the oscillator ofthe master station sothat a frequencyseparation is maintainedbetween it vself and the. oscillator of theselected station equal to the selected intermediate frequency.

- Y EDWARDW; HEROLD.`

, c'. In a two-way radio communication system y

